The technique described herein relates to an impulse generator that generates an extremely thin pulse, and more specifically, to an impulse generator that utilizes a nonlinear transmission line of which a diode is connected.
An impulse output from an impulse generator includes frequency components in a wide range from direct current to high frequencies, and therefore, an impulse generator is widely utilized in a wide band radio communication system or a measuring system for generating a sampling pulse of an oscilloscope.
FIG. 1 is a diagram showing an example of an impulse generator in a wide band radio communication system. As shown in FIG. 1, a baseband (oscillation) signal generated by a baseband signal generator 11 is modulated by an impulse generated by an impulse generator 12 and after being filtered by a band pass filter 13, it is amplified in a transmission amplifier 14 and transmitted from an antenna 16 via a transmission/reception switching switch 15. On the other hand, radio waves received by transmission antenna 16 are transmitted to a receiving amplifier via transmission/reception switching switch 15 and amplified therein, and then, filtered by band pass filter 13, detected in a detector 19, and regenerated in a baseband signal regenerator 20.
As shown schematically, in the signal transmitted from antenna 16, parts where an impulse is present correspond to a data value “1” and parts where no impulse is present correspond to a data value “0”. In order to increase the amount of information that can be transmitted, the time is required to be shortened (data width) for a datum and therefore to make an impulse narrower.
Among impulse generators, an impulse generator that utilizes a nonlinear transmission line is capable of generating an extremely thin pulse, the half value width of which is several picoseconds due to the effect of reduction in pulse width by the non-linearity of the transmission line. The impulse generator can be applied to a next generation wide band radio communication system or measuring system.
An impulse generator using a nonlinear transmission line is described in, for example, “Generation of 3.5-ps fall-time shock waves on a monolithic GaAs nonlinear transmission line”, Madden, C. J.: Rodwell, M. J. W.; Marslanad, R. A.; Bloom, D. M.; Pao, Y. C., IEEE Electron Device Letters vol. 9, no. 6 Page(s): 303-305 1988.
FIG. 2A and FIG. 2B are diagrams showing an impulse generator that uses the nonlinear transmission line described in the above document: FIG. 2A shows its configuration; and FIG. 2B shows the characteristics (input signal and output signal) of the impulse generator. As shown in FIG. 2A, an impulse generator that uses a conventional nonlinear transmission line has a pulse generation source 21 that generates a pulse signal, a nonlinear transmission line 22 in which a plurality of transmission line units, such as a transmission line unit having a unit line unit P1 and a diode D1, a transmission line unit having P2 and D2, a transmission line unit having P3 and D3, etc., are connected in series, a terminating resistor 23, and an input resistor 24. As shown in FIG. 2B, when a pulse from the pulse generation source 21 is input to the transmission terminal of the line, in the course of propagation of the pulse signal through the line, the fall of the signal gradually becomes steeper due to the non-linearity effect of the diode.